Cabin pressure control



Nov. 29, 1960 w. B. KLEMPERER CABIN PRESSURE CONTROL 4 Sheets-Sheet 2Original Filed April 6, 1942 ELECTRON/C 9:44)

, INVENTOR. IVOLF'GA/VG 5.16:2 slums-25R A rroe/vsy.

Nov. 29, 1960 w. is. KLEMPERER Re. 24,900

CABIN PRESSURE ,CON'IROL Original Filed April 6, 1942 INVENTOR. WOLFGANG5. mama/95x? i BY I 1 -i A rrak'win w. B. KLEMPERER Re. 24,900

CABIN PRESSURE CONTROL Nov. 29, 1960 4 Sheets-Sheet 4 Original FiledApril 6 49 ELECTRON/C llllll INVENTOR. WbLF/l/VE r31 KZEMPEAER UnitedStates Patent Ofiice Reissuecl Nov. 29, 1960 CABIN PRESSURE CONTROLWolfgang B. Klemperer, Los Angeles, Calif., assignor to Douglas AircraftCompany, Inc., Santa Monica, Calif.

Original No. 2,549,690, dated Apr. 17, 1951, Ser. No. 437,921, Apr. 6,1942. Application for reissue Dec. 1, 1953, Ser. No. 395,640

48 Claims. (Cl. 981.5)

Matter enclosed in heavy brackets appears in the original patent butforms no part of this reissue specification; matter printed in italicsindicates the additions made by reissue.

My invention relates to aircraft pressure cabins and more particularlyto apparatus for controlling and regulating the pressure therein.

Generally, a pressure cabin is a livable compartment, in which the airpressure is artificially controlled and regulated at values usuallyabove the ambient atmospheric pressure prevailing at flight altitude.The pressure cabin is not, as a rule, hermetically sealed, inasmuch asmeans are required both to take air into and to exhaust air from thecabin in order to maintain a livable pressure while the aircraft fliesthrough high strata of air too thin for safely sustaining respiration.Moreover, these means are capable of reestablishing pressureequalization prior to landing.

If a cabin shell is constructed sulficiently strong to permit sea levelpressure to be maintained therein at any altitude the particularaircraft can attain, the only pressure regulation problems are thosecaused by diflerences of altitudes at the points of departure andarrival. A cabin so constructed would of necessity be rather heavy andthereby reduce the economic eificiency of the aircraft.

Most aircraft passengers, however, can readily tolerate altitudes in therange of 5,000 to 10,000 feet, and, in view of this fact, it isstructurally and mechanically advantageous to design a pressure cabinfor a certain moderate pressure differential. It is then desirable togradually reduce the cabin pressure during ascent at a lesser apparentrate of climb than that of the aircraft, but in a manner such that thepermissible pressure differential is never exceeded. Similarly, duringdescent, the cabin pressure may be gradually raised in order to equalthe existing ambient atmospheric pressure shortly before landing.

The principal object of my invention is to provide an aircraft cabinpressure control system which complies with such limitations ofpermissible pressure differences between the interior of the cabin andthe ambient or flight atmosphere as may be dictated by passengercomfort, strength considerations or limitations of compressor power.

Another object is to provide a pressure regulating system which willeffect changes in cabin differential pressure inversely proportional tochanges in flight altitude pressure of the aircraft.

A further object is to provide a pressure regulating system which willeffect changes in cabin absolute pressure directly proportional tochanges in flight altitude pressure of the aircraft.

Another object is to minimize the rate of pressure changes to whichoccupants of the cabin are subjected while the aircraft climbs ordescends at a high rate or encounters bumpy air.

Still another object is to provide such a rate of pressure changecontrol means which, subject to a preselected differential pressurelimit, will permit or induce a change of pressure within the cabin,whether an increase or a decrease, at a preselected rate and regardlessof the change or rate of change of ambient or flight altitude pressure.

Further objects are: to provide a system for controlling the pressurewithin a cabin; to provide a control for antomatically and/or manuallyregulating the pressure Within a cabin; and to provide an altitude-ratiomechanism for controlling the pressure within a cabin.

Still further objects are: to provide mechanism for minimizing the rateand/or degree of cabin pressure changes; to provide adjustable mechanismfor setting the altitude above which the pressure cabin shall operate;and to provide a relatively rugged, inexpensive, and efficient cabinpressure control system.

Other and further objects will become apparent as the descriptionproceeds.

For a clearer understanding of my invention, reference may be had to thedrawing in which:

Fig. l is a perspective schematic view of an embodiment of my cabinpressure control system, a fragmentary portion of the aircraft beingshown in phantom;

Fig. 2 is a partially sectional and partially schematic view ofcomponents of the pressure control system including a cabin pressureregulator, lag control, cabin rate of climb meter, cabin altimeter, andthe electrical system for controlling cabin outlet valves;

Fig. 3 is a sectional view of another embodiment of .a cabin pressureregulator;

Fig. 4 is a sectional view of a third embodiment of a cabin pressureregulator.

Fig. 5 is a schematic diagram of an outlet valve limit switch system forcontrolling blower air delivery;

Fig. 6 is a partially sectional and partially schematic View of apressure regulating system including a cabin rate of climb meter and acabin altimeter, the cabin pressure regulator of Fig. 2 being renderedinoperative in this embodiment.

Referring now to the drawings, an airplane 6 having wings, fuselage,control surfaces, power plant, etc. is equipped with a cabin 8 adaptedto withstand a desirable pressure differential or, in other words, to besupercharged. Pressure in the cabin is supplied by one or more blowers10 and is regulated primarily by one ,or more controlled cabin airoutlet valves 12 which may be connected, as shown, by a cable 13 forsimultaneous operation. The blowers receive fresh air preferably fromthe nose of the fuselage through a ram duct system 14, and delivercompressed air to the cabin through ducts 16 or .a conventional heatingand ventilating system. The duct system 14 comprises three conduits, twoof which lead directly to the blowers 10, and the other one leadsdirectly to the cabin duct system. The latter conduit is the largest ofthe three and incorporates a check valve 15 which is adapted to closethe aft portion of this duct to incoming air as soon as the blowersbegin operating and build up a pressure in the cabin greater than theflight ram pressure. In fact, my invention is such that there need be nodifference in the distribution of fresh air or its temperature controlmechanism, whether or not the cabin is supercharged. In order toaccomplish supercharging or pressurizing, however, it is necessary thatthe cabin, cabin air exhaust valves, ducts and other associated parts bedesigned to withstand a pressure difference.

The controlled cabin air outlet valves 12, 12 are supplemented by largeroverhead exhaust outlets 18 for discharging suflicient vitiated air fromthe cabin and lavatories in unsupercharged flight. These large outletsare especially needed to insure ample ventilation in hot weather. WhileI have shown only two controlled cabin air outlet valves 12, 12,theremay be three or more in a passenger airplane, depending upon thecabin size,

and these may be interconnected by suitable mechanism so as to actpartly in series, partly in parallel. A plurality of these valves,differently located, is advantageous because, when flying supercharged,it is desirable to exhaust the air mostly from the lavatories ordressing rooms which may be situated at opposite ends of the cabin.

When ascending, and desiring to supercharge, the large outlets 18 areclosed and the quantitative outlet control is turned over to the smallervalves 12, 12 which can be more accurately regulated and whichpreferably discharge into such unsupercharged fuselage portions asbaggage and cargo compartments, thereby not only heating these port-ionsbut also precluding the possibility of icing occurring in the outlets,The control of the valves 12, 12 can be operated manually as by a handle20 in case of emergency, but normally this control is effectedautomatically by a servo system, broadly referred to as 22, which isresponsive to or controlled by a cabin pressure regulator 24.

The present preferred embodiment of such a cabin pressure regulator is,in effect, an altitude-ratio control which tends to regulate or changethe cabin absolute pressure directly proportional to changes in ambientflight pressure. In most cases, a flight schedule is prepared beforetake-off wherein is determined the altitudes which the airplane willattain and the altitudes at which the airplane will cruise, and thecabin pressure regulator can be adjusted accordingly to set the cabinsupercharger system in operation when desired.

Up until the time the supercharger system begins operating, the cabinpressure and flight pressure are substantially equal and the altitudeset on the regulator is then the line of demarcation from an equalizedpressure condition inside and outside the cabin. This set altitude maythen be termed the equalizing altitude from which the pressuredifferential is built up as the airplane ascends.

The regulator 24 comprises a case 26, the interior of which is subjectedthrough the conduit 130 to the absolute pressure within the aircraftcabin. The case 26 houses a pair of coaxially mounted pressure sensitiveunits 28 and 30. The unit 28 is an evacuated bellows or aneroid and isresponsive to changes in the cabin absolute pressure. The unit 30 is acapsule exteriorly subjected to cabin pressure while the interiorthereof is connected by conduit 31 to ambient flight pressure. Thiscapsule thus is responsive to changes in the difference between cabinabsolute pressure and ambient flight pressure that is responsive tochanges in cabin differential pressure.

A contact arm 32 is pivotally connected at its one end 34 to a bracket36 fixed to an inner wall surface of the case 26. This arm is alsopivotally connected intermediate i'ts ends at 38 to an extensioncoaxially carried by the aneroid 28. The free end of the contact arm 32is disposed between a pair of spaced contacts 40 and 42 and this end asthe arm is pivotally moved because of expansion or contraction of thepressure responsive units 28 and 30, will move between and intoengagement with one or the other of the spaced contacts 40 and 42.

To indicate the regulator setting a scale 44, together with an index,not shown, is provided on the face of the instrument. Adjustment of theregulator, that is the setting of the equalizing altitude, isaccomplished by a knob 46 fixed to the outer end of a small shaft 47rotatably carried by the one wall of the case 26. The inner end of theshaft 47 is threadedly engaged in a tapped opening formed in the onewall of a slide member 48 held against rotation. The slide member 48carries the contacts 40 and 42 and it will be seen that as the shaft 47is rotated the slide member 48 will move in one direction or the otherdepending upon the direction of rotation of the shaft 47. This movementof the slide member 48 obviously will vary the position of the contacts40 and 42 relative to the end of the arm 32 disposed between the same.The scale 44 is formed about its edge face as clearly shown in Figure 24 with a plurality of teeth to permit the scale to be driven through thepinion shown mounted to the shaft 47.

While I have shown in Figure 2 the preferred embodiment of the regulator24, the arrangement may also be such that the contacts 40 and 42 arefixed and the fulcrum of the lever arm 32 adjustable relative thereto,as shown in the form of the regulator illustrated by Figure 3.

In addition to this embodiment, there are at least two otherinterchangeable and feasible adaptations of the two pressure sensitiveunits 28, 30, the common feature of all three being that cabin pressure,flight altitude pressure and their difference are effective upon theinstrument. One of these other adaptations is shown in Fig. 3, whereinthe units 28, 30 perform the same function as in Fig. 2 but are nolonger superposed and therefore may be of different sensitivity as willbe later explained. The third adaptation is shown in Fig. 4 wherein theunit 28 is of the same type as in Figs. 2 and 3, that is an aneroid, butis now responsive to flight altitude pressure, and the unit 30 is apressure capsule exposed to the pressure differential between fiightaltitude pressure and cabin absolute pressure, the flight altitudepressure being connected into the regulator case through the conduit 31and the cabin pressure being connected to the interior of the unit 30 bythe conduit 130.

If an altitude ratio control of, say, 1 to 2 is desired, that is, cabinpressure controlled substantially halfway between flight altitudepressure and equalizing altitude pressure, and if the sensitivity of thetwo regulator units is alike, they can be merely superposed as shown inFig. 2. If, however, the sensitivityis not the same, a lever system suchas that shown in Fig. 3 must be introduced for connecting the units 28,30 to the lever arm 32 in order to obtain the desired 1 to 2 ratio.

The regulator in effecting control of cabin absolute pressure performsthree functions, one at a time; it may energize a valve closing circuit49 of the servo system when an increase in cabin pressure is needed; orit may energize a valve opening circuit 50 of the servo system whencalling for a decrease of cabin pressure; or it may energize neither theincrease nor decrease circuits when the cabin pressure is substantiallythe pressure called for by the predetermined ratio of flight altitudepressure to cabin pressure.

The regulator 24 controls the servo system 22 through the arm 32 as thesame is pivotally moved in response to the changes in the pressures towhich units 28 and 30 are subjected. This control action is effected bythe end of the lever 32 which is moved into and out of engagement withthe spaced contacts 40 and 42. The contact 40 forms a part of the valveclosing circuit 49 while contact 42 is connected into and forms a partof valve opening circuit 50. The arm 32 is electrically connected to alead 32a which may be called the grounding conductor for the regulator24.

The servo system includes an electric motor 51 of the reversible splitfield series type adapted to drive, in either direction, suitable geartrains operatively connected to move the valves 12. The motor 51 may beoperated by energization of either a field coil circuit 52 or a fieldcoil circuit 53 from some suitable power source such as a battery 54 toopen or close the valves 12 depending upon the direction of rotation ofthe motor.

As will be hereinafter shown, the directional control of the motor andconsequently the valves 12 may be effected lthrough movement of thecontact arm 32 as it is pivotally moved because of contraction orexpansion of the pressure units 28 and 30 in response to changes in thepressures to which these units are subjected.

The servo system 22 also includes a relay 55, which is essentially apower amplifier in that very small currents from a battery 56 can beused to bring about a flow of relatively large current in the motorfield circuits 52 and 53 respectively. The relay 55 comprises two fieldcoils 57 and 58 connected respectively to the control circuits 50 and49. Energization of the control circuit 49 and its associated coil 53will cause the armature 59 of the relay 55 to move into engagement witha contact 60 connected into the motor field circuit 52 to energize thesame. Energization of the field coil circuit 52 causes the motor 51 todrive the discharge valves 12 towards closing position and similarlyenergization of the control circuit 50 will cause the armature 59 tomove into engagement with a contact 61 of the field coil circuit 53 toresult in energization of that circuit to bring about opening movementof the discharge valves 12. The two centering springs not only hold thearmature 59 in the balanced or central position as shown in Figure 2 inwhich neither control circuit is energized, but are also effective tomove the armature 59 into its center position whenever both controlcircuits are simultaneously energized.

To prevent overloading of the contacts forming a part of controlcircuits 49 and 50, an electronic relay schematically indicated at 62may be used.

At high altitude the position of the outlet valves can serve to indicatethe air flow rate. Consequently a servo control can be attached to theoutlet valve mechanism to be actuated when the valves open or closebeyond two or more set stations. A motor 68 actuated by this control isprovided for each blower '10 to decrease or increase the flow of freshair by more or less throttling the flow or by slowing down or speedingup the blowers.

The principles of operation of all embodiments of the regulator hereinshown and described are the same. For example, if the equalizingaltitude of the instrument is set at 2000 feet, the contact arm 32, solong as that altitude is not exceeded, will be held by the aneroid 28 inengagement with the contact 42. Engagement of the arm 32 with thiscontact, it will be remembered, results in energization of the valveopening relay coil so that the valve 12 will be held open to equalizecabin pressure with ambient flight pressure during ascent of theairplane from a landing field to an altitude of 2000 feet. As theaircraft approaches 2000 foot altitude, the aneroid 28 in expanding willmove the contact arm 32 out of engagement with the contact 42 and as the2000 foot altitude is reached the now further expanded aneroid will movethe .arm into engagement with the contact 40. When the arm 32 is engagedwith the contact 40, the valve closing relay is energized to bring aboutclosing movement of the valve 12. As the valve is moved toward itsclosed position, cabin absolute pressure will consequently increase andthe increasing pressure tends to collapse the aneroid 28 to move thecontact arm 32 away from contact 40. Disengagement of the arm 32 fromcontact 40 arrests further movement of the valve and if cabin absolutepressure falls below the equalizing pressure of 2000 feet, as theaircraft ascends beyond that altitude, the arm 32 will again move intoengagement with the contact 40 to again increase cabin absolutepressure. It will thus be seen that the aneroid 28 seeks to maintaincabin absolute pressure substantially that of the preselected equalizingaltitude as the aircraft ascends beyond that altitude.

If the aneroid 28 was the only instrument controlling operation of thevalve 12, cabin pressure would be maintained substantially constantunder the control of that instrument. The differential pressure capsule30, however, is also operatively connected to control the valve 12 andonce the aircraft has ascended beyond 2000 feet altitude, increasingcabin diiferential pressure brings about a collapsing movement of thedifferential capsule 30 in opposition to the force produced by theexpanding aneroid. It will thus be seen that the position of the arm 32is conjointly controlled by the aneroid 28 and the diiferential pressureresponsive capsule 30 to so vary the rate of air discharge from thecabin that cabin absolute pressure changes in direct proportion tochanges in ambient flight pressure.

High rates of climb or descent of the airplane may be encountered whenthe pilot maneuvers over or under clouds, or when vertical air currentsin an unstable atmosphere carry the airplane up or down; then even thefractional rate of climb or descent apparent in the cabin, as governedby the pressure regulator, may be too rapid for physiological comfort.To avoid this a lag control incorporated in the flight altitude pressureconduit 31 makes it possible to produce a lag between the change offlight altitude pressure and cabin pressure. This control consists of athermally insulated air volume bottle 72 and a needle valve 74. Thebottle 72 functions to decrease the pressure sensitivity of the ambientpressure in the conduit, the thermal insulation preventing sudden cabintemperature variations from inducing erratic air pressure variationswithin the bottle. The valve 74 controls the amount of opening in theconduit 31 and consequently the amount of response to flight pressurechanges on the part of the unit 30. When the lag valve is wide open nolag in pressure change is effected and the unit 30 follows quickly theoutside pressure cranges at the flight pressure to cabin pressure ratio.If the lag valve is tightly closed, the flight pressure unit 30 of theregulator becomes inoperative, the regulation then tending to maintainconstant absolute cabin pressure. When the lag valve is partly closed,the action is intermediate and the cabin pressure will eventually followflight altitude pressure changes toward the predetermined ratio, butwith some lag inasmuch as the air can but slowly escape into or out ofthe regulator until considerable back pressure develops. Thus, suddenflight altitude changes of short duration are smoothed out and kept fromappreciably affecting the cabin pressure, whereas prolonged altitudechanges will be followed eventually.

As previously mentioned, it is possible to vary the ratio of cabinpressure to flight pressure control within reasonable limits. One methodof accomplishing such a ratio change is illustrated in Figure 4. In theratio control instrument of this embodiment, an adjustable fulcrum isprovided between the lever arm 32 and a connecting rod 63 pivotallyinter-connecting the pressure responsive units 28 and 30. The fulcrumadjusting mechanism may comprise a roller 64 adapted for rollingmovement along the rod 63 to thus vary its position relative to thelever arm 32. The roller is actuatable by a knob 65 carried by a stubshaft 66 rotatably extending through the case of the regulator. Theinner end of the shaft 66 is threadedly engaged in a bore of a boss 67pivotally connected to the push-pull rod 68 carrying the roller 64. Theprinciple of such a ratio Changing mechanism is to vary the relativeeffectiveness of the pressure units 28 and 30 which principle obviouslymay be accomplished in various ways.

The system thus far described is sufiicient to accomplish certain of theobjects of the invention. However, I have also incorporated in thesystem a cabin rate of climb meter '76 and cabin altimeter 78 which maybe used at Will to make supercharging functions more flexible undercertain operating conditions. The cabin rate of clirrrb meter may beused in conjunction with the cabin altimeter to accomplish superchargingmore or less manually, in which case the regulator 24 is disconnectedfrom the electrical hookup by a switch 80 and the system then isessentially as depicted by Fig. 6. This system will be later described.

In addition to this, the cabin rate of climib met-er 76 may be used inconjunction with the lag valve 74 and for a similar purpose, in whichcase the cabin altimeter is disconnected from the electrical system by aswitch 82. The cabin rate of climb meter 76, fully illustrated in Figure6 but only schematically shown in Figure 2 is exposed to cabin pressureand is connected into the electrical hookup by a switch 84. The meter isof the conventional type except that its pressure sensitive unit,designated by the numeral 85, is adapted to actuate a lever 87 insteadof an indicating needle. Also, a pair of new spaced electrical contacts86, 88 are provided, the separation of which can be adjusted by a knob90. When the contacts are widely separated, the meter does not interferewith quick response of the cabin pressure to flight altitude pressurechanges in that the lever is unable to touch either of the contacts 86,88 before an extensive change has taken place. However, when thecontacts are closely adjusted, the meter does interfere because thelever touches one or the other of the contacts more quickly dependingupon the distance between them, thereby opposing any rapid cabinpressure changes.

In addition to the possible adjustment of the contacts relative to eachother by means of the knob 90, another knob 104 is adapted to move bothcontacts relative to the lever, and this knob is geared to the rate ofclimb meter dial for setting the desired rate of climb or descent.Contact 86 may be termed the cabin climb or pressure decrease rate limitcontact, and 88 the cabin descent or pressure increase rate limitcontact, the device being so arranged in the outlet valve controlsystem, as shown in Fig. 2, that in the event of regulator 24 demandingan increased cabin pressure and the rate of climb meter 76 demanding alower pressure, relay 55 will balance and open both circuits, therebystopping or damping the valve action in response to the speed of climbor descent. For example, if it is desired to adjust the equalizingpressure of the regulator 24 to a higher equalizing altitude, the outletvalves 12, 12 would immediately begin opening in order to seek the newratio between cabin pressure and flight altitude pressure. As the cabinpressure rises, the rate of climb meter 76, being responsive to the rateof cabin pressure change, will actuate the system through the cabinclimb limit contact 86 if the rate of ascent is in excess of the setlimiting rate of climb, which limit is determined by the distance thatthe ascent limit contact is set from zero. This would in turn cut outthe valve opening circuit of the outlet valve control. Conversely, ifthe equalizing pressure setting of the regulator is lowered, the systemis actuated by the cabin descent limit contact of the meter when therate of descent is excessive, and the valve closing circuit is cut out.

To more fully explain the operation of the rate of climb meter 76 in thesystem disclosed in Figure 2, it will be seen that contact 86 iselectrically connected to the control circuit 49 by a lead 86A. Thecontact 88 and the control circuit 50 are electrically interconnected bya lead 88A. As the lever arm 87 is electrically connected by a lead 87Ato the grounding conductor 32A, it Will be seen that the meter 76 canalso control energize.- tion of the relay 55.

If in any flight of the aircraft, the ambient flight pressure isincreasing or decreasing at such a rate that the regulator 24 ineifecting its ratio control brings about a rate of pressure changewithin the cabin in excess of the preselected rate of change, the rateof climb meter 76 can override the regulator 24. For example, if the arm32 of the regulator has been moved into engagement with the contact 42to energize the coil 57 of the relay 55 to bring about opening movementof the valves 12 and the pressure within the cabin begins to decrease ata rate in excess of the preselected one, the arm 87 of the meter 76 willmove into engagement with the contact 88 and thus also energize the coil58 of the relay 55. As previously explained, the centering springs, whenboth coils of the relay 55 are energized, will move the armature 59 intoits center or balanced position between the contacts 60 and 61. Thismovement of the armature obviously results in de-energization of themotor field circuits 52 and 53 to arrest further movement of the valves12 and consequently further increase in the rate of pressure changewithin the cabin.

It can also be pointed out that if the contact arm 32 is disposedbetween, that is, engaging neither of the contacts 40 and 42, the rateof climb meter can then act as a primary control and will bring aboutmovement of the valves 12 to prevent a rate of pressure change in excessof the preselected one.

Both the manually operated lag mechanism and thecabin rate of climbmeter are utilized for causing the" cabin pressure to follow the flightaltitude pressure in a: ratio reduced from the predetermined regulatorcon' trolled ratio if the flight altitude change is too rapid forphysiological comfort. used simultaneously in flight altitudecommunication to the regulator, thereby providing not only a positiverate of climb and descent limit or pressure decrease and increase limit,but also a nominal lag for substantially eliminating cabin pressurechanges during temporary and rapid flight altitude pressure changes.Either lag or damping device can be set before take-off and reset at anytime during flight.

As previously stated, in order to control the supercharging of the cabinmore flexibly than is possible with the automatic regulator 24, theelectrical control circuit can be opened by switch 80, whereupon theregulator 24 is rendered inoperative, and the cabin altimeter switch 82and rate of climb meter switch 84 are closed, the system then conformingwith Fig. 6.

The altimeter used is of the conventional type except that its pressuresensitive unit, designated by the numeral 97, is adapted to actuate alever 99 instead of the indicator needle ordinarily incorporated insimilar instruments. This lever is provided to close the electricalcircuits at contacts 98100, the separation of which can be adjusted by aknob 102. The operating principle with respect to the lever and thecontacts is identical with that of the rate of climb responsive unit,the difference between the two being that the rate of climb unit limitsthe rate of increase and decrease of cabin pressure, Whereas thealtimeter controls the maximum and minimum pressures in the cabindepending on the setting of the contacts relative to the lever 99. Inaddition to the possible adjustments of the contacts relative to eachother by means of the knob 102, a knob 107 is provided to adjust bothcontacts relative to the lever. This latter knob is geared to thealtimeter dial for setting the con tacts to the desired altitude. Theterm altitude in this instance, however, is used as referring to cabinpressure in that if the altimeter dial is set at 10,000 feet, the unitwill maintain a pressure in the cabin corresponding to that found at10,000 feet altitude in standard air even though the actual flightaltitude may be, for example, 12,000 feet.

The cabin rate of climb meter new functions to limit the cabin rate ofclimb or descent or pressure decrease or increase until a cabin pressureequivalent to the altitude previously set on the altimeter is reached,whereupon the altimeter will halt the climb or descent and tend tomaintain the cabin pressure constant to that altitude. In other words,although the system is attempting to induce a change in cabin pressureindependently of the actual flight path of the aircraft, the cabin rateof climb meter actuates the decrease and increase servo systems at theset rate of speed, as the airplane climbs and descends until the desiredpressure altitude, as selected on the altimeter, is reached. When thisaltitude is reached the altimeter will open or deenergize the decreasecircuit if the airplane is ascending or cut out the increase circuit ifthe airplane is descending. No ratios are used in this mode ofsupercharger control, nor are any pressure sensitive units necessaryother than those customary in conventional rate of climb meters andaltimeters. In fact, this embodiment may be described as effecting aclimb schedule control as distinguished from the previously disclosedaltitude ratio control.

Before such a climb schedule controlled super-charged flight, the cabinaltimeter upper limit contact 98 is set by the knob 107 to the maximumdesired cabin pressure Both these lag devices may be altitude, say,10,000 feet, and the contacts on the cabin rate of climb meter are setby means of a knob 104 to a definite value, say, 300 feet, per minute.While the airplane is climbing, and the supercharging system isfunctioning, the cabin pressure will decrease at the set rate until theset pressure altitude is attained, at which time the altimeter lever 99will connect with contact 98 and, through the servo system, willmaintain the desired pressure.

When the cabin pressure conforms with the pressure altitude setting thecabin rate of climb meter contacts 86, 88 may be set to zero rate ofclimb and the lower altimeter limit contact 98 and the higher altimeterlimit contact 100 may be set close together by means of the knob 102,thereby substantially preventing any cabin pressure fluctuations in thatthe levers S7 and 99 would immediately connect with one or the other oftheir respective contacts and operate the valve control through theservo system.

When ready to descend, the lower altimeter limit is reset to an altitudeslightly above the field of destination and the cabin rate of climbmeter contacts are set to the desired rate of descent or cabin pressureincrease. While the airplane is descending, the cabin pressure willgradually rise to and linger at the pressure of the set altitude untilthe flight altitude reaches the same level, at which time thesupercharging system is turned off and the cabin is opened to ambientatmospheric pressure.

It will thus be seen that the system of the present invention will infact induce a pressure change within the cabin even though the aircraftmay be flying in level flight. This is possible with all embodiments ofthe system disclosed for, as previously explained, whenever theregulator 24 or the altimeter 78 is reset in flight the cabin pressurewill tend to reach as quickly as possible the reset pressure value, butis prevented from rapidly changing because of the action of the rate ofclimb meter 76-. Whether the rate of climb meter 76 is connected intothe system so as to act as a vetoing or overriding instrument or it isso connected that it acts as a primary control instrument, it is alwaysoperative to limit the rate of pressure change within the cabin to thepreselected rate.

A number of safety features must be observedin an aircraft cabinpressure regulation system to insure passenger com-fort and operationsafety. For example, safety valves 106 are provided in the large exhaustoutlets l8 and are set to relieve if the pressure diflerential exceedsthe design limit. Such diflerential pressure responsive valves have beenheretofore used to limit cabin differential pressure and one such valveis shown in Figure 2 of the United States patent to Gregg No. 2,002,057.A valve of this type may also be arranged to cut out the fresh air flowincrease control and/or the outlet valve closing circuit. Non-returnvalves 108 are provided in the supercharger delivery ducts to preventreverse flow in event of a compressor failure. A check valve 15 isarranged to open and thus prevent any appreciable suction in the cabinwhen the airplane descends to altitudes below the pressure equalizationaltitude. This valve is preferably located in the ram duct wherein uponstarting to supercharge it will close as soon as the cabin pressureexceeds the ram pressure.

The operation of the automatic pressure differential superchargingsystem as controlled by the regulator 24 will now be described.

Before beginning a supercharged flight, the operator determines themaximum altitude the airplane will or may attain, say 17,000 feet, andfrom this he determinem the pressure altitude at which he maysupercharge the cabin while at maximum flight altitude without reachingthe permissible pressure ditferential of, say, 3 pounds per square inchbetween cabin pressure and flight altitude pressure, and yet obtain ahigh value of passenger comfort. With this maximum difierential pressure, in the particular example above given, the cabin pressure altitudewould be 9,000 feet. He then determines the equalizing altitude to whichhe may set the regulator, assuming that the altitude ratio incorporatedin the regulator was already fixed at, say, 1 to 2, for the normalflight conditions over his route. In the case of the above example, thisequalizing altitude would result as 2X9000l7000=1000. If the operatordoes not wish to begin supercharging at this altitude, perhaps becausehis take-off or landing field may already be situated higher, say, at1500 feet, then he will set his equalizing altitude slightly higher,say, at 2000 feet, and the cabin will then attain a slightly higherapparent altitude, for example, 9500 feet, when the airplane reaches itspeak altitude of 17,000 feet.

If the cabin rate-of-climb meter is connected into the system, thisshould be set as previously described to the esired maximum rate ofclimb and descent or pressure decrease and increase. These settings maybe changed at any time in flight.

As the airplane ascends to the equalizing altitude, the blowers 10 areturned on and the large cabin exhaust outlets 18 are closed, thecontrollable outlets 12, 12- remaining wide open. The lag valve 74 isusually set to minimum lag or fully open.

When the equalizing altitude is reached, the pressure regulator beginsto move the outlet valves and, with increasing flight altitude, thesevalves gradually move toward closed position. The cabin pressuredifferential rises and when it surpasses ram duct pressure the ram ductcheck valve 15 closes.

As the airplane is leveled oif for cruising at relatively high altitude,the cabin pressure remains substantially constant at the predeterminedratio between flight altitude pressure and the set equalizing altitudepressure. The damping controls may be set to greater sluggishness tominimize unintentional cabin pressure changes as the airplane encountersrising and descending air currents, or the cabin-rate-of-climb meter maybe set to lower limits of climb and descent or pressure decrease andincrease.

For normal descent, the damping controls are reset to low lag in orderto allow the cabin rate of descent or pressure increase to follow theflight rate of descent at the predetermined ratio. During descent, ifthe cabin climb meter is inoperative, the lag should be adjusted tosluggish when a temporary high rate of descent of the airplane isplanned. However, if the climb meter is operative, the lag valve may beleft fully open and the rate-ofclimb meter will restrain the cabindescent or pressure increase to the set rate. When the set equalizingaltitude is reached, the valve outlets 12, 12 are open, the ram ductcheck valve 15 opens, the blowers are shut off and the large cabinexhaust outlets 18 are opened.

Various departures from normal operation are feasible and are left tothe discretion of the operator when he is confronted with unusualconditions. For example, in climbing it may be desirable to delaystarting the blowers until after the set equalizing altitude pressurehas been passed, in which case the damping of the regulator should beadjusted to sluggish or the climb limits set low while the cabinpressure temporarily increases to its called for value. When the cabinpressure finally begins to decrease, the leg adjustment and/or the climbmeter should e reset to allow the normal flight schedule to be followed.The operator may also decide to land supercharged, in which case he mayreset the equalizing altitude slightly below the field of destinationand reduce the pressure slowly while taxiing.

My pressure regulation system is essentially automatic whilesupercharging and therefore requires none other than normal attention.However, manual emergency control is available at any time and anydegree of semiautomatic control can be adopted if desired; one methodbeing the variation of the equalizing altitude setting and another byhand manipulation of the outlet valves. Also the regulator 24 may beswitched off and the pressure controlled by the rate of climb meter andthe altimeter as previously described.

While I have described my invention in its present embodiments, it willbe obvious to those skilled in the art, after understanding myinvention, that various changes may be made therein without departingfrom the scope thereof. I aim in the appended claims to cover all suchmodifications or changes.

I claim as my invention:

1. In an aircraft cabin adapted to be supercharged above the ambientatmospheric pressure, supercharging means, comprising a blower, at leastone outlet valve for discharging vitiated air from the cabin, aservomotor adapted to control said valve, a regulator operative toactuate said motor in response to any departure of cabin pressure from avalue functionally correlated with flight altitude pressure, meansadapted to vary the functional relation between flight altitude pressureand cabin pressure, means adapted to govern the flow of superchargingair into said cabin, means adapted to adjust the said regulator to a setequalizing altitude above which supercharging begins and below whichsupercharging ceases, means adapted to limit and delay the response ofsaid motor to excessive or sudden variations of the functional relationof flight altitude, means adapted to govern the flow of superchargingair from said cabin, and means for assuming manual control of said valvein event of failure of said motor.

2. In an aircraft, a cabin pressure regulating device for controllingcabin pressure altitude at a reduced ratio from flight pressurealtitude, said device including in operative combination at least twocoacting pressure sensitive units, the first being responsive to cabinpressure and the second being responsive to both cabin pressure andflight pressure, a servo system for controlling cabin air flow, meansfor transmitting the eifect of pressure reactions of said coacting unitsto said servo system for controlling said ratio, and means for retardingthe sensitivity of the second said unit to flight pressure, wherebysudden flight pressure variations are prevented from causingcorresponding sudden cabin pressure variations.

3. In an aircraft, a cabin adapted to be supercharged, a ramming airintake duct leading to said cabin, a supercharging blower adapted toincrease the pressure of the incoming air, an outlet valve adjustable tovary the cabin pressure with relation to the incoming blower pressure, aregulating device sensitive to pressure differences between flightaltitude pressure and cabin pressure and adapted to control said outletvalve to maintain a predetermined ratio between cabin pressure andflight altitude pressure, as gauged from a set equalizing altitudepressure, a servomotor for operating said outlet valve, said servomotorbeing actuated in response to pressure variations in said regulatingdevice, a second servomotor for varying the delivery of the superchargerblowers if the valve is unable to adequately control the pressuredifferential, means within the outlet valve to control the second saidmotor, and an adjustable lag means for preventing rapid changes inflight altitude pressure from eifecting a change in cabin pressure at arate too rapid for physiological comfort, said lag means comprising avalve for restricting the connection between flight altitude pressureand the said regulating device.

4. in an aircraft, a cabin pressure regulating device for controllingcabin pressure altitude at a reduced ratio from flight pressurealtitude, said device including in operative combination at least twocoacting pressure sensitive units, one unit being responsive to changesin cabin pressure, the other responsive to changes in the differencebetween cabin pressure and flight pressure, means for controlling cabinair flow, means for transmitting the effect of pressure reactions ofsaid coacting units to said control means for controlling said ratio, arate of climb regulating means for limiting the rate of decrease orincrease of cabin pressure, and means for setting the limiting rates,the rate of climb regulating means being adapted to override thecontrolling influence of said coacting pressure sensitive units uponsaid control means, thereby preventing pressure change in the cabin at arate in excess of the set limiting rates.

5. In an aircraft, a cabin adapted to be supercharged, at least oneblower for supercharging said cabin, at least one outlet valve forcontrolling the amount of supercharging, an automatic regulator forcontrolling said outlet valve, the regulator comprising a pair ofpressure sensitive coacting units, one unit being responsive to cabinpressure, the other responsive to changes in the diflerence betweencabin pressure and flight pressure whereby a pressure ditferential isobtained between flight altitude pressure and cabin pressure, the saiddiflerential being controlled by the opening and closing of said outletvalve in response to pressure reactions of the said coacting units, anda lag means comprising a rate of climb meter sensitive to cabinpressure, said climb meter acting, in event of rapid changes in flightaltitude pressure such as rapid climb or descent, to override thecontrol of the regulator with respect to said outlet valve and prevent asimilarly rapid change in cabin pressure by limiting the cabin pressurechange to a set rate, compatible with physiological comfort.

6. In an aircraft, a cabin adapted to be supercharged, a ramming airintake duct leading to the cabin, at least one blower adapted toincrease the pressure of the incoming air, an outlet valve adjustable tovary the cabin pres sure with respect to the incoming blower pressure, aregulating device sensitive to pressure differences between flightaltitude pressure and cabin pressure and adapted to control said outletvalve to maintain a predetermined ratio between cabin pressure andflight altitude pressure as gauged from a set equalizing altitudepressure, a servomotor actuated in response to pressure variations insaid regulating device, said servomotor operating said outlet valve, asecond servomotor for varying the delivery of the said superchargingblower, means within the said outlet valve for controlling the secondsaid servomotor, a valve means controlling the reaction of flightpressure upon the said regulating device whereby the rapidity of cabinpressure changes may be varied or halted with respect to flight altitudepressure changes, and a rate of climb meter adapted to control the rateof decrease or increase of cabin pressure irrespective of the rate offlight altitude pressure decrease or increase, such control beingaccomplished by overriding the influence of the said regulating devicein the control of said servomotor operating said outlet valve.

7. A cabin pressure regulating device comprising an adjustable dial forsetting an. altitude at which cabin pressure will be equalized withflight pressure, a pair of spaced contacts, a pair of coacting pressuresensitive units, a lever pivotally connected to said pressure sensitiveunits and adapted for contacting either or neither of said spacedcontacts, and means connected with the said dial for relativelyadjusting the said contacts and lever, the combination being responsiveto cabin pressure and flight pressure and operative to maintain thecabin pressure substantially at a ratio of equalizing pressure minusflight pressure to equalizing pressure minus cabin pressure.

8. A cabin pressure regulating device comprising an adjustable dial forsetting an altitude at which cabin pressure will be equalized withflight pressure, a pair of spaced contacts, a pair of pressure sensitiveunits, a lever connecting the sensitive units and a lever indirectlyconnected to the first said lever and adapted to contact either orneither of the said spaced contacts, and a third lever adapted to moverelatively to the first said lever and the second said lever, for thepurpose of changing the fulcrum of the first said lever as it moves,whereby the effect of reactions of the said pressure sensitive units maybe varied with respect to the second said lever moving between thespaced contacts, the combination being sensitive to cabin pressure andflight pressure and operative to maintain the cabin pressure at apredetermined ratio to the flight pressure as gauged from a setequalizing pressure.

9. In an aircraft, a cabin adapted to be supercharged and having anoutlet, blower means for supplying air to said cabin at a pressurehigher than that of the ambient flight atmosphere, air flow controlmeans for varying the cabin pressure, rate of climb regulator means togovern the rate of decrease or increase of cabin pressure, means forvarying the rate of decrease or increase as governed by said regulatormeans, means for limiting cabin pressure to a set pressure altitude,means for varying the said pressure altitude, and a servo systemoperative upon said airflow control means and responsive to saidregulator means and said pressure limiting means to control the said airflow.

10. In an aircraft, a cabin adapted to be supercharged and having anoutlet, a blower for supplying air to said cabin at a pressure higherthan that of the ambient flight atmosphere, a valve in said cabinoutlet, a rate of climb meter sensitive to cabin pressure, means foradjustably setting said meter to govern the rate of decrease or increaseof cabin pressure, an altimeter sensitive to cabin pressure, means foradjustably setting a limiting cabin pressure, and a servo systemresponsive to said climb meter and said altimeter for opening andclosing said outlet valve, thereby controlling the pressure in saidcabin in accordance with the settings of said climb meter and saidaltimeter.

11. In an aircraft, a cabin adapted to be supercharged and having acontrollable outlet, a blower for supp-lying air to said cabin at apressure higher than that of the ambient flight atmosphere, a rate ofclimb meter sensitive to cabin pressure and having adjustable means forsetting a cabin pressure rate of decrease and increase, a primary servosystem responsive to said rate of climb meter for opening and closingsaid controllable outlet, thereby controlling cabin pressure rate ofdecrease and increase, an altimeter sensitive to cabin air pressure andhaving adjustable means for setting a limiting cabin pressure altitude,and a second servo system responsive to said altimeter for overridingsaid primary system when the cabin has attained the set pressurealtitude.

12. In combination with an aircraft pressure cabin, means to supply airunder pressure within the cabin, normal means to regulate and vary thepressure therein automatically under the influence of and generally inaccordance with change of external pressure, auxiliary means, includinga rate-of-pressure-change element, operable automatically under theinfluence of change of cabin pressure to overrule said normal means andto limit the rate of pressure change, and means always operable tooverrule the normal means and the auxiliary meaans to limit the pressuredifference between cabin pressure and external pressure to a preselectedone.

13. Mechanism for controlling change of pressure within an aircraftcabin, comprising means operable to create and control a difference ofpressure within the cabin over the external pressure, an air chamberwithin said cabin having a restricted opening in it, a wall movableunder the influence of a pressure difference internally and externallyof the air chamber, due to a change of pressure within the cabin at arate in excess of the capability of the restricted chamber opening torelieve the pressure within the air chamber, and means operativelyassociated with said movable wall, and operatively connected to saidfirst means to govern its operation for limiting the rate of pressurechange within the cabin.

14. Pressure control means for a chamber exposed to varying exteriorpressures, comprising valve means communicating the interior of saidchamber with the exterior thereof, a motor for operating said valvemeans, and a rate of pressure change device in said chamber comprising apressure sensitive element having one side thereof in directcommunication with the pressure within said chamber and the other sidethereof in restricted communication with said chamber pressure, whereby,upon a predetermined rate of change of pressure within said chamber,said element is actuated to energize said motor to operate said valvemeans to close communication between the interior and exterior of saidchamber.

15. In an aircraft cabin, a vent valve, a motor for operating saidvalve, first pressure-sensitive means responsive to cabin pressure onone side and sub-atmospheric pressure on its other side operativelyconnected to actuate said motor, second pressure-sensitive meansresponsive to cabin pressure on one side and to atmospheric pressure onits other side also operatively connected to actuate said motor, andpressure-responsive means having one side thereof directly subjected tocabin pressure and the other side thereof in restricted communicationwith said cabin operatively connected to said motor to override saidfirst and second means when cabin pressure changes at excessive ratesduring changes in the altitude of flight.

16. Mechanism for regulating the pressure within an aircraft body forhigh altitude flights, and adapted to be sealed at high or mediumaltitudes against escape of pressure from within, under the influence ofa pressure differential above the ambient pressure at such altitudes,comprising means operable to create such a pressure differential withinthe sealed cabin, a rate-of-pressure-change element responsive to changeof pressure within the cabin, means operable at will, in anticipation ofa change in altitude, and consequent change in cabin pressure, to inducea change in cabin pressure for altering such pressure differential,independently of the rate of change of the ambient pressure, due tochange or lack of change of altitude, and means controlled by saidrate-of-change elemerit for governing said inducing means to limit therate of change of pressure within the cabin during such inducingoperation.

17. Mechanism to control aircraft cabin pressures comprising, incombination with means to supply air under pressure to the cabin,differential-pressure responsive means operable at all altitudes toprevent the cabin pressure exceeding a selected pressure above theexternal pres sure, absolute-pressure responsive means subject to cabinabsolute pressure operable at a selected altitude to maintain cabinpressures substantially constant, up to the limit of differentialpressure set by the differential-pressure responsive means, and meansoperable at will, and overriding the absolute-pressure responsive means,but subject to the limiting control of the differential-pressureresponsive means, to effect or control the rate of change of cabinpressure.

18. Mechanism to control aircraft cabin pressures, comprising, incombination with means to supply air under pressure to the cabin, anormal automatic control system including an absolute-pressureresponsive means automatically operable at a selected altitude toinitiate an increase of cabin pressure relative to external pressure,and a differential-pressure responsive means automatically operable atall altitudes to prevent increase of cabin pressure beyond a selecteddiiferential over extrenal pressure, and therefore at a given altitudeimposing a maximum limit on the increase initiated by theabsolute-pressure responsive means, and controlling cabin pressures ataltitudes above such given altitude, and further in combinationtherewith a manual control system including means to override at willthe absolute-pressure responsive means and to initiate a change of cabinpressure, whether rise or fall, independently of altitude, but arrangedto be limited by the dilferential-pressure responsive means, whereby thediiferential limit set by the latter is never exceeded by the manualcontrol system nor by the automatic control system.

19. Mechanism to control aircraft cabin pressures, comprising, incombination with means to supply air under pressure to the cabin, and anoutlet to discharge air from the cabin, valve means operable to controlair movement through and pressure within the cabin, means operableautomatically, to operate said valve means to maintain a substantiallyconstant cabin pressure, differentialpressure responsive means operableautomatically at all times upon the attainment of a selecteddifferential of cabin pressure above external pressure for limiting suchdifferential to the selected value, and means manually operable at alltimes to operate said valve means to decrease outflow and thereby toincrease cabin pressure above such substantially constant value, or toincrease outflow and thereby to decrease cabin pressure below suchsubstantially constant value, between a lower limit fixed by theexternal pressure, and an upper limit fixed by saiddifferential-pressure responsive means, and at a selected rate ofpressure change.

20. In combination with an aircraft pressure cabin, normally operablemeans to maintain the pressure therein substantially equal to externalpressure up to a selected altitude, to substantially maintain within thecabin a pressure corresponding to such selected altitude during flightbetween that altitude and a selected higher altitude, and to maintainsubstantially the attained differential of cabin pressure over ambientpressure during flight above the second selected altitude, and auxiliarycontrol means operable to limit the rate of cabin pressure change inflight from a higher to a lower altitude, or vice versa, independentlyof and regardless of the rate of cabin pressure change which wouldotherwise be imposed by the normal control means at the rate of descentor ascent chosen.

21. In combination with an aircraft pressure cabin, normally operablemeans to maintain the pressure therein substantially equal to externalpressure up to a selected altitude, to substantially maintain within thecabin a pressure corresponding to such selected altitude during flightbetween that altitude and a selected higher altitude, and to maintainsubstantially the attained diiferential of cabin pressure over ambientpressure during flight above the second selected altitude, auxiliarycontrol means operable to limit the rate of cabin pressure change inflight from a higher to a lower altitude, or vice versa, independentlyof and regardless of the rate of cabin pressure change which wouldotherwise be imposed by the normal control means at the rate of descentor ascent chosen, and means to adjust the auxiliary control means toselect and effect control at different rate of pressure change.

22. In combination with an aircraft pressure cabin structure having aknown resistance to bursting under the influence of a higher pressureinternally than externally, means to supply air under pressure withinthe cabin, means operable to control and produce a pressure differentialof cabin pressure over external pressure, a rate-of-pressure-changecentral to govern the action of the pressure controlling means, andthereby to govern the rate of pressure change within the cabin,regardless of change or rate of change of external pressure, and adifferential-pressure control means operative to limit the pressuredifference possible of attainment to a safe value within the burstingstrength of the cabin structure.

23. Mechanism for controlling change of pressure within an aircraftcabin, comprising pressure-responsive means operable automatically toeffect a change of cabin pressure, and thereby to establish a pressuredifferential between the pressure within the cabin and the exterioratmospheric pressure, and a rate-of-pressure-change element responsiveto rapid change of pressure within the cabin and operatively connectedto the differential-establishing means, whereby upon such rapid rate ofpressure change it is automatically operable to retard the 16 action ofsaid pressure-responsive means, thereby to limit the rate of pressurechange within the cabin.

24. Mechanism to control aircraft cabin pressure, comprising, incombination with means to supply air under pressure to and to dischargeair from the cabin, three pressure responsive means, one whereof issensitive to the pressure differential of cabin pressure over externalpressure, and always operable to prevent such differential exceeding aselected value, the second operable to regu late cabin pressure withinthe differential thus determined, and the third being sensitive to rateof pressure change, to restrict any change of pressure, within thepredetermined differential, automatically to a predetermined rate,independently of the rate of air supply to or discharge from the cabinor the actual diiference between cabin pressure and external pressure orthe rate of change of such difference.

25. Mechanism to control aircraft cabin pressure, comprising, incombination with means to supply air under pressure to and to dischargeair from the cabin, three pressure responsive means, one whereof issensitive to the pressure differential of cabin pressure over externalpressure, and always operable to prevent such differential exceeding aselected value, the second operable to regulate the cabin pressureWithin the differential thus determined, and the third being sensitiveto rate of pressure change, to restrict any change of pressure, withinthe predetermined differential, automatically to a predetermined rate,independently of the rate of air supply to or discharge from the cabinor the actual difference between cabin pressure and external pressure orthe rate of change of such difference, and means to adjust said thirdpressure reponsive means, to preselect any one of various rates ofpressure change.

26. Mechanism to control aircraft cabin pressures, comprising, means tosupply air under pressure within the cabin, differential-pressureresponsive means always operable to prevent the cabin pressure exceedinga selected pressure above the external pressure, and settable meanssensitive to rate of pressure change within the cabin, operable toeffect change of cabin pressure, Within the limiting differential fixedby said differential-pressure responsive means, at a preselected ratewhich is independent of all factors other than rate of supply.

27. In combination with an aircraft body capable of flight at highaltitudes, and having a cabin structurally formed to resist an allowablepressure difference between cabin pressure and external pressure, whichpressure difference is not in excess of a fraction of the total pressuredifference between sea level and the aircrafts ceiling, means operableto create a pressure differential within the cabin, not greater than thestructurally allowable pressure dilference, an element subject to cabinpressure, and sensitive to rate of change thereof, and means operable inresponse to the rate-of-pressure-change element to prevent pressurechange in response to said first means at a rate in excess of apredetermined rate.

28. In combination with an aircraft capable of flight at high altitudes,and having a cabin structurally formed to resist an allowable pressuredifference between cabin pressure and external pressure which is not inexcess of a fraction of the total pressure difference between sea leveland the aircrafts ceiling, means to supply air under pressure Within andcontinuously to discharge such air from the cabin, to decrease suchpressure dilference, means to control the cabin pressure tosubstantially maintain it at a value which, with relation to externalpressure, is not greater than the allowable pressure difference, andmeans operable to regulate the rate of pressure change within the cabin,regardless of whether such change occurs by reason of ascent or descent,and consequent change of external pressure, or by reason of change inthe rate of supply of air under pressure, or by reason of change in therate of discharge of air from the cabin.

29. A pressure control device for controlling the pressure in the cabinof an aircraft comprising, in combination, means forming a port, a valvemember movable relative to said port-forming means for controlling flowof fluid through said port, a bellows held stationary at one end andconnected at its other end to a movable connecting element, a secondbellows connected at one end to said movable connecting element andhaving at its other end an operative association with said valve elementsuch that movement of said other end controls the movement of said valveelement, means for subjecting the exterior of both of said bellows tocabin pressure, and means for subjecting the interior of one of saidbellows to ambient pressure, the other bellows being evacuated.

30. A pressure control device for controlling the pressures in the cabinof an aircraft comprising, in combination, means forming a port, a valvemember movable relative to said port-forming means for controlling fiowof fluid through said port, a bellows held at one end stationary andconnected at its other end to a movable element, an evacuated bellowsconnected at one end to said movable element and operatively connectedat its other end to said valve member, means for subjecting the exteriorof both of said bellows to cabin pressure, and means for subjecting theinterior of said first bellows to ambient flight pressure.

31. A pressure control device comprising, in combina tion, a port, avalve seat surrounding said port, a valve member cooperating with saidvalve seat for controlling the flow of fluid through said port, andpressure responsive means for controlling the operation of said valvemember, said pressure responsive means including a pressure responsivemember operatively connected to said valve member and subjected on oneside to the pressure at one side of said valve seat and on its oppositeside to a subatmospheric pressure, and a second pressure responsivemember connected to said first pressure responsive member and actingthrough the latter on said valve member, said second pressure responsivemember subjected continuously on opposite surfaces thereof to the pressures at opposite sides of said valve seat.

32. In a device for controlling the cabin pressures of an aircraft,valve means adapted to vent the cabin interior, means for controllingsaid valve means, a device responsive to cabin pressures and operativeon reduction of cabin pressure to a value corresponding to apredetermined height for transmitting movement to said control means toaffect control of said valve means to vary venting to seek to maintainthe cabin pressure substantially constant, and a device responsive tothe differential in pressure between the cabin pressure and the exteriorpressure for actuating said means controlling said valve means andoperative at a predetermined pressure differential for furthertransmitting movement to said valve control means to vary venting, saiddevices so arranged with respect to each other that one of said devicestransmits its individual valve positioning movements to said valvecontrol means through the other device, and the latter device reactsagainst the former when transmitting its individual valve positioningmovements to said valve control means.

33. In a device for controlling the cabin pressures of an aircraft,valve means adapted to vent the cabin interior, pressure responsivemeans operative on reduction of cabin pressure to a value correspondingto a predetermined altitude for actuating said valve means to varyventing to seek to maintain the cabin pressure substantially constant,and a second pressure responsive .means responsive to the differentialin pressure between the cabin pressure and the exterior pressure forfurther actuating said valve means to vary venting, each of saidpressure responsive means embodying an expansible chamber controldevice, one operatively connected to said valve means and the otherdevice yieldingly connected to operate said valve means through thefirst device, one of said control devices having one side thereofsubjected to the cabin pressure and the opposite side to asubatmospheric pressure and said other control device having one sidethereof subjected to cabin pressure and its opposite side subjected toatmospheric pressure.

34. A sealed cabin for an aircraft provided with valve meanscommunicating the interior of the cabin with the exterior thereof, andmeans comprising a pressure sensitive element having one side thereof indirect communication with said cabin pressure and an opposite sidethereof in restricted communication with said cabin pressure responsiveto and actuated during a predetermined rate of change of pressure withinsaid cabin during a rapid rate of climb or descent of said craft whensaid valve means is open for operating said valve means to closecommunication between the interior and exterior of said cabin.

35. Mechanism for controlling change of pressure within an aircraftcabin, comprising means operable to create and control a diiference ofpressure within the cabin over the external pressure, an air chamberwithin said cabin having a restricted opening in it, a wall movableunder the influence of a pressure difference internally and externallyof the air chamber, due to a change of pressure within the cabin at arate in excess of the capability of the restricted chamber opening torelieve said pressure diiference, and means operably associated withsaid movable wall to determine limits within which the rate of pressurechange in the cabin is to be held.

36. An aircraft compartment having blower means therefor, valve meanscommunicating the interior of the compartment with the exterior thereof,control means for operating said valvemeans to maintain the pressureswithin the compartment at predetermined values with respect to varyingexterior pressures, and means having one side thereof in directcommunication with the compartment pressure and an opposite side thereofin re stricted communication with the compartment pressure operativeduring a predetermined rate of change of pressure within saidcompartment when the compartment interior and exterior are incommunication for controlling said valve means independently of saidcontrol means.

37. An aircraft compartment having blower means therefor, valve meanscommunicating the interior of the compartment with the exterior thereof,control means for operating said valve means to maintain the pressureswithin the compartment at predetermined values with respect to varyingexterior pressures, and a rate of change of pressure device having oneside thereof in direct communication with the compartment pressure andan opposite side thereof in restricted communication with thecompartment pressure operative during a predetermined rate of change ofpressure Within said compartment when the compartment interior andexterior are in communication for closing said valve means.

38. Pressure control means for a chamber exposed to varying exteriorpressures, comprising valve means communicating the interior of saidchamber with the exterior thereof, and means comprising a resilientmember having one side thereof in direct communication with said chamberpressure and an opposite side thereof in restricted communication withsaid chamber pressure responding to a predetermined rate of pressurechange within said chamber when said chamber interior and exterior arein communication for operating said valve means to close communicationbetween the interior and exterior of said chamber.

39. Pressure control means for a chamber exposed to varying exteriorpressures, comprising valve means communicating the interior of saidchamber with the exterior thereof, and means including a compressibleand expansible member having the inside thereof in restrictedcommunication with the chamber pressure and the outside thereof indirect communication with the chamber pressure responding to apredetermined rate of pressure change within said chamber when saidchamber interior and ex- 19 te rior are in communication for operatingsaid valve means to close communication between the interior andexterior of said chamber.

40. An aircraft having a compartment provided with valve meanscommunicating the interior of the compartment with the exterior thereof,a reversible motor for operating said valve means, and means including apressure sensitive resilient member having one side thereof in directcommunication with the pressure within said chamber and the other sidethereof in restricted communication'with said chamber pressure, whereby,upon a predetermined rate of pressure change within said chamber duringa rapid rate of climb of said craft, said member is actuated to energizesaid motor to operate said valve means to close communication betweenthe interior and exterior of said compartment.

[41. An aircraft having a compartment provided with valve meanscommunicating the interior of the compartment with the exterior thereof,and means including a pressure sensitive element having one side thereofin direct communication with the pressure within said compartment andthe other side thereof in restricted communication with said compartmentpressure, whereby, upon sudden chamber pressure decrease causing apredetermined rate of change of pressure within said compartrnent duringa rapid rate of climb of said craft, said element is actuated in onedirection to operate said valve means to close communication between theinterior and exterior of said compartment, and whereby, upon a suddencompartment pressure increase causing a predetermined rate of change ofpressure within said compartment during a rapid rate of descent of saidcraft, said element is actuated in a second direction to operate saidvalve means to likewise close communication between the interior andexterior of said compartment] 42. An aircraft sealed compartment havingblower means therefor, valve means communicating the interior of thecompartment with the exterior thereof, electrical means for said valvemeans, control means for energizing said electrical means to actuatesaid valve means to maintain the pressure within said compartment in apredetermined relation with respect to the pressure exterior. of saidcompartment, and means comprising a resilient member having one sidethereof in direct communication with said compartment pressure and anopposite side thereof in restricted communication with said compartmentpressure actuated during a predetermined rate, of change of pressurewithin said compartment for energizing said electrical means to operatesaid valve means and close communication between the interior andexterior of said compartment.

43. A sealed cabin for an aircraft provided with valve meanscommunicating the interior of the cabin with the exterior thereof, andmeans comprising a pressure sensitive element having one side thereof indirect communication with said cabin pressure and an opposite sidethereof in restricted communication with said cabin pressure responsiveto and actuated during a predetermined rate of change of pressure withinsaid cabin during a rapid rate of climb or descent of said craft whensaid valve means is open for operating said valve means to closecommunication between the interior and exterior of said cabin.

44. In a system of pressure control for a sealed chamber, a continuouslyenergized blower means for building up pressure in said chamber, valvemeans providing communication between the inside and outside of saidchamber, control means within said chamber for operating said valvemeans to maintain the pressure within said chamber at predeterminedvarying values with respect to a varying exterior chamber pressure, andrate of change of pressure means including a pressure sensitive elementhaving one side thereof in direct communication with the pressure withinsaid chamber and the other side thereof in restricted communication withsaid chamber 20 pressure, whereby, upon a predetermined rate of changeof pressure within said chamber said element is actuated to operate saidvalve means and close communication between the interior and exterior ofsaid chamber.

45. A sealed cabin for an aircraft having a continuously energizedblower for building up pressure within said cabin, valve means fornormally communicating the interior of the cabin with the exteriorthereof, a reversible motor for operating said valve means, meansincluding a pressure sensitive element responding to cabin pressure onlyand a second pressure sensitive element responding to the differentialof the cabin pressure and the atmospheric pressure outside thereof forenergizing said motor in one direction to operate said valve means whenthe pressure within the cabin has reached a predetermined value to closecommunication between the interior and exterior of said cabin, saidelements being operative to energize said motor in the oppositedirection opening said valve means to permit communication of theinterior of said cabin with the exterior thereof when the pressure builtup by said blower exceeds a predetermined amount, and means, including apressure sensitive element subjected on one side to cabin pressure andon the opposite side to a volume of air in restricted communication withthe interior of said cabin, operative during a predetermined rate ofchange of pressure within said cabin for energizing said motor to closesaid valve means.

46. An aircraft cabin pressure control system COIIIPIIS- ing means fordelivering air to said cabin under a pressure greater than ambientflight pressure, a valve for discharging air from said cabin, means foroperating said valve to vary the rate of air discharge from said cabinrelative to the rate of air delivery to said cabin whereby the absolutepressure within said cabin may be varied, a first pressure sensitivemeans responsive to changes in cabin absolute pressure operativelyconnected to said valve operating means and adapted to actuate the sameto seek to maintain cabin absolute pressure substantially constant, asecond pressure sensitive means responsive to changes in the diflerencebetween cabin absolute pressure and ambient flight pressure, and meansoperatively interconnecting said second pressure sensitive means andsaid valve operating means for progressively opposing the action of saidfirst pressure sensitive means on said operating means as ambient flightpressure decreases to thereby impose a conjoint action resulting fromchanges in cabin absolute pressure and cabin diflerential pressure onsaid valve operating means whereby cabin difierential pressure will becontrolled to change substantially inversely proportional to changes inambient flight pressure.

47. An aircraft compartment pressure control comprising means fordelivering air to said compartment under a pressure greater than ambientflight pressure, means for discharging air from said compartment, meansfor varying the rate of air discharge from said compartment relative tothe rate of air delivery to said compartment whereby the absolutepressure within said compartment may be varied, means, including a firstcapsule subject to cabin absolute pressure and a second capsule subjectto cabin differential pressure coacting through an interconnectingmeans, made operative upon said aircraft reaching a predeterminedpressure altitude for controlling said last named means for regulatingthe absolute pressure in said compartment in such a manner as to changesaid absolute pressure directly proportional to changes in ambientflight pressure, and means for preselecting the pressure altitude atwhich said controlling means is made operative, said preselecting meansbeing changeable during flight of said aircraft and operableindependently of said control means whereby said pressure. altitude atwhich said control means is made operative may be altered during flightof said aircraft without altering the said proportion.

48. An aircraft compartment pressure control comprising means fordelivering air to said compartment under a pressure greater than ambientflight pressure, means for discharging air from said compartment, meansfor varying the rate of air discharge from said compartment relative tothe rate of air delivery to said compartment whereby the absolutepressure Within said compartment may be varied, means, including a firstcapsule subject to cabin absolute pressure and a second capsule subjectto cabin diiferential pressure coacting through an interconnectingmeans, made operative upon said aircraft reaching a predeterminedpressure altitude for controlling said last named means for regulatingthe absolute pressure in said compartment in such a manner as to changesaid absolute pressure directly proportional to changes in ambientflight pressure.

49. An aircraft having a compartment provided with valve meanscommunicating the interior of the compartment with the exterior thereof,and means including a pressure sensitive element having one side thereofin direct communication with the pressure within said compartment andthe other side thereof in restricted communication with said compartmentpressure, whereby, upon sudden compartment pressure decrease causing aprede- References Cited in the file of this patent or the originalpatent UNITED STATES PATENTS 2,208,554 Erice July 16, 1940 2,407,257 DelMar Sept. 10, 1946 2,620,719 Price Dec. 9, 1952 FOREIGN PATENTS 514,055France Nov. 8, 1920

